1. Field
The present application relates generally to light emitting diodes, and more particularly, to an efficient LED array.
2. Background
A light emitting diode (LED) is a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, a doped region of the semiconductor can have predominantly electrons or holes, and is referred to as an n-type or p-type semiconductor region, respectively. In LED applications, the semiconductor includes an n-type semiconductor region and a p-type semiconductor region. A reverse electric field is created at the junction between the two regions, which cause the electrons and holes to move away from the junction to form an active region. When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and combine. When electrons combine with holes, they fall to lower energy levels and release energy in the form of light.
During operation, a forward voltage is applied across the p-n junction through a pair of electrodes. The electrodes are formed on the semiconductor material with a p-electrode formed on the p-type semiconductor region and an n-electrode formed on the n-type semiconductor region. Each electrode includes a wire bond pad that allows an external voltage to be applied to the LED.
Generally, a device having multiple LED chips is created by mounting closely spaced LED chips on a ceramic substrate. Unfortunately, the closely spaced LED chips may interfere with each other and result in reduced light output. Also, a ceramic substrate is used because the LED chips have thermal and electrical paths that come in contact with each other. For example, an LED chip may have electrical contacts on both top and bottom surfaces so that when the chip is mounted to a substrate, both heat and electricity may pass to the substrate. Thus, the ceramic substrate provides electrical insulating properties while allowing some heat to pass. Unfortunately, the ceramic substrate doesn't provide a very efficient thermal path so that heat generated by the closely spaced LED chips may degrade light output. To facilitate heat dissipation, the ceramic substrate may be mounted to an aluminum heat spreader, which is turn is mounted to an additional heat sink. This arrangement is costly and results in more complicated manufacture.
Accordingly, there is a need in the art for improvements in LED devices to increase light output, provide efficient heat dissipation, and simplify manufacture.